Polyethylenimines (PEIs) are promising non-viral vehicles for effective protection and delivery of short/small interfering RNA (siRNA), a therapeutic tool used to knock down mRNA levels, thereby arresting the translation of cancer-related proteins. Not only do PEIs prevent siRNA degradation during transfection, but also their strong buffer capacities allow the PEIs/siRNA complexes to follow an endosome-escape mechanism for mRNA silencing. However, the toxicity of current PEIs-based vehicles is high, and the efficiency of siRNA release is low. Branched PEIs (BPEIs) have been initially demonstrated to act as siRNA-delivery vectors. The transfection efficiency and toxicity of BPEIs, however, are strongly correlated with their molecular weights. BPEIs with high molecular weights display enhanced efficiency but also dramatically increased toxicity. In contrast, linear-like PEIs (LPEIs) exhibit less toxicity and elicit a weaker inflammatory response than BPEIs. Unfortunately, the release efficiency of siRNA from the LPEI-based vehicles is still insufficient.
In the past decade, most researches focused on reducing the cytotoxicity of BPEIs through structure modification, rather than enhancing the release efficiency of LPEIs. Post-modification of BPEIs can significantly decrease their toxicity; various building blocks such as polyethylene glycol (PEG) segments and alkyl groups can attenuate the positive charges of the tertiary amines. Nevertheless, the modified BPEIs still present adverse side effects, such as intracellular stress and mitochondrial alternations leading to cell death. LPEIs are much safer than BPEIs, but current time-consuming synthesis and purification methods limit the use of LPEIs in bio-related applications. Recently, a high-throughput and organic-solvent-free protocol for LPEIs synthesis was developed to overcome these limitations (Shu-Yi Lin, et al., “One-pot synthesis of linear-like and photoluminescent polyethyleneimine for intracellular imaging and siRNA delivery” Chem. Commun. 2010, 46, 5554-5556; and Supplemental materials thereof, both of which are herein incorporated by reference in their entireties).
Therefore, a heretofore unaddressed need exists in the art to address the deficiencies and inadequacies, especially in connection with development of PEIs for efficient delivery and release of siRNA within cells.